1. Field
Example embodiments of the inventive concept relate to a high frequency X-ray generator. More particularly, example embodiments of the inventive concept relate to a “high frequency X-ray generator capable of improving quality of X-ray image using a multiple switching circuit.”
2. Description of the Related Art
Generally, an X-ray generator for medical and industrial purpose is a device which generates an X-ray having predetermined quality and dose through an X-ray tube.
A traditional X-ray generator may a perform switching operation at a rate of more than 15 kHz at a high frequency inverter, and provide the generated voltage to a transformer and a rectifier circuit to multiply and rectify. The transformer multiplies the provided voltage according to a turns ratio of a first side and a second side. The rectifier circuit performs a rectifying of an AC voltage from the transformer. The traditional X-ray generator generates a high voltage to apply the X-ray tube according to the above steps.
The traditional X-ray generator may be classified into an X-ray generator with quasi-resonant converter type and an X-ray generator with full resonant converter type.
The X-ray generator with quasi-resonant converter type has a circuit structure that power is applied to both of anode and cathode. In the X-ray generator with quasi-resonant converter type, one inverter and one transformer generates anode high voltage and cathode high voltage, and the sum of the anode high voltage and the cathode high voltage is feedback controlled. However, for this reason, a voltage deviation due to characteristic differences between an anode high voltage circuit and a cathode high voltage circuit may be caused. The voltage deviation is small when the high voltage is low power, whereas the voltage deviation is about 10% when the high voltage is high power.
The X-ray generator with full resonant converter type uses PFM (Pulse Frequency Modulation) method that X-ray output is controlled by modulating switching frequency with maintaining a uniform on-period. An X-ray image is influenced by AC pulsation and rise time which are output voltage characteristics of the X-ray generator. The output voltage characteristics are determined by a tube-voltage output-frequency and dynamics of a controller. As the tube-voltage output-frequency is getting higher, the AC pulsation and the rise time is getting lower, so that clear X-ray image may be obtained. Thus, the X-ray generator with full resonant converter type which can heighten the switching frequency is preferred. However, in the X-ray generator with full resonant converter type, the switching frequency is heightened when low power X-ray is outputted, and the switching frequency is lowered when high power X-ray is outputted to control the X-ray output. Thus, the maximum switching frequency may be heightened, but relationship between the switching frequency and the output voltage or relationship between the switching frequency and the output power is nonlinear, so that responsiveness may be worse than the PWM (Pulse Width Modulation) method.